Cortical crosstalk

By Jef Akst
Cortical Crosstalk
Scientists are eavesdropping on the brain’s conversations in search of
clues underlying complex behaviors.
Recorded waveforms of neural activity.
Courtesy of Earl Miller
The brain is the most complex organ in the human body, but for years, available
technology greatly limited scientists’ interpretation of how the billions of
neurons act in concert to create complex behav

By Jef Akst | October 1, 2009

Cortical Crosstalk

Scientists are eavesdropping on the brain’s conversations in search of
clues underlying complex behaviors.

Recorded waveforms of neural activity.

Courtesy of Earl Miller

The brain is the most complex organ in the human body, but for years, available
technology greatly limited scientists’ interpretation of how the billions of
neurons act in concert to create complex behaviors. Recent advances in neuronal
recording technology, however, along with the invention of the Pentium
processor–based computer capable of digitizing the data at a much higher rate
than ever before, have enabled brain research to progress at an increasingly rapid pace.

In 2007, neuroscientist Earl Miller of the Massachusetts Institute of Technology
and his postdoc Timothy Buschman pushed the evolving technology to a new level with
rhesus macaques. By implanting up to 50 electrodes, which recorded activity from neurons
in three different brain regions simultaneously, the study (this month’s Hot
Paper) was one of the first to compare entire populations of neurons from multiple areas
of the primate brain. As the monkeys performed different visual search tasks, the
researchers compared the activity of neurons in the parietal and frontal cortices. They
found that in search trials where the item the monkeys were looking for was extremely
obvious—so-called bottom-up processing—the parietal cortex reacted
first, followed by the frontal cortex. In contrast, when the monkey must actively search
for the target—so-called top-down processing—the signal flowed in
the opposite direction.

A few years earlier, neuroscientists Michael Goldberg and James Bisley of
Columbia University in New York had found that the parietal cortex was involved in both
top-down and bottom-up processing,1 “but we
didn’t know which way [the signal] was going,” says Bisley, who
currently works at the David Geffen School of Medicine at the University of California
Los Angeles. The 2007 study was the first to demonstrate such directionality in
attention-related behavior.

While Miller wasn’t the first to record from multiple areas in the
primate brain simultaneously, he “really pushed the envelope” with
regard to the number of electrodes, says neuroscientist Bob Desimone of the
Massachusetts Institute of Technology. “[Using] multiple electrodes [to]
record from different [primate] brain regions made this study a major step
forward,” agrees neuroscientist John Duncan of the MRC Cognition and Brain
Sciences Unit (CBU) in England.

Since the publication of this month’s Hot Paper, the use of
multielectrode recording has spread like wildfire through the primate neuroscience
community. “It certainly started something that I think has been very good for
the field,” Bisley says. “I wouldn’t call [the technique]
common, but I think everyone is trying to get going in that direction.”

Scientists are now using multielectrode approaches to tackle a wide range of
complex topics, including attention, coordination, and decision making. “There
are hardly any primate labs that aren’t playing around with multielectrode
recording in some way,” says Desimone.

Rats to macaques

The use of multiple electrodes in different regions of the mammalian brain began
in the mid-1990s, when researchers employed the technique to shed light on the precise
relationships between groups of neurons.

In 1995, neuroscientist Miguel Nicolelis of Duke University Medical Center
permanently implanted dozens of hair-like electrodes—known as
microwires—to concurrently record from five different brain areas of rats. He
identified predictable cycles of synchronized activity during tactile stimulation and
just before the rats’ whiskers started exploring their
environment.2

In 1998, Nicolelis used his microwires to record from three different cortical
regions of owl monkeys, all of which showed nearly simultaneous activation upon tactile
stimulation.3 Starting in 2001, Desimone and his colleagues
published a series of studies in which they used multiple, movable electrodes to record
neuronal activity within the visual areas of macaques.4 All of
this laid the foundation for Buschman and Miller’s 2007 paper, and a
concurrent study by neuroscientist Trichur Vidyasagar of the University of
Melbourne.5

The new wave

Other neuroscientists have since used Buschman and Miller’s technique
to further explore how different brain regions work together to coordinate behavior. In
2008, neuroscientist Bijan Pesaran of New York University and colleagues recorded the
frontal and parietal cortices in rhesus macaques and learned that the two areas were
more in sync when monkeys had freedom to make their own choices versus when they had to
follow instructions, suggesting these areas may be part of a “decision
circuit.”6 In May of this year,
Desimone’s group found that the frontal eye fields—an area believed
to respond to visual stimuli—and the V4 area of the visual cortex showed a
similar pattern of activity when a monkey was presented with colored dots on a screen.
This finding suggests that communication between these two areas may play a role in
attention.7 Most recently, Buschman and Miller published a
study demonstrating that coordinated activity within the frontal eye fields may help
regulate when monkeys shift their attention while performing difficult search
tasks.8 Scientists have also begun to use multielectrode
techniques to understand the intricate neural signals necessary for controlling
prosthetic limbs.

“It’s pretty clear that a lot of labs are very excited about
the potential that [multiple electrodes] have,” Pesaran says. Multielectrode
recording is “the tool of the future,” Nicolelis agrees.
“In a few more years, we’ll be able to record [30,000] or 40,000
cells [simultaneously].”

Data derived from the Science Watch/Hot Papers database and the Web
of Science (Thomson ISI) show that Hot Papers are cited 50 to 100 times
more often than the average paper of the same type and age.

Comments

Good article. I remember when the Buschman and Miller paper appeared. I thought it was an exciting use of new technology. I am glad it is a "hot" paper and people are citing it so much. I also remember that awful letter that Schall wrote about it. He didn't seem to read the paper carefully and got a lot of things wrong. I guess it was the knee-jerk reaction of an backwards-thinking guy resisting progress.

What is the code the neural system uses to lay down a revoverable memory? Recording the neural spikes does not seem adequate. Neural spikes are fine for understaning the principle of muscular activity, but not for understanding the purpose of muscular activity. I would not for a moment distract from recording 100,000 neural spikes, but suggest the code (the real message) may be in the frequency (and volume) of spiking. The analogy would be a symphony orchestra, (the relation of the frequencies of the instruments not their volumes or locations).\nJust a suggestion into just how a brain may work. God may Not be in the detail, but in the pattern of coordination.\n\nJust an ignorant observer...sorry about that. IB

It is misleading to say that parietal cortex responds before frontal, or vice-versa. Each region contains many cell types, organized into layers within the cortex. Response latencies vary widely among individual cells and layers. \n\nFor example, response latencies in primary visual cortex (V1) range from 30 to 100 msec. Visual latencies in prefrontal cortex can be as short as 50 msec. Hence, many prefrontal neurons are activated by visual stimuli well before many neurons in V1. Depending on which cells one recorded in each area, one could conclude either that signals flow from V1 to prefrontal cortex, from prefrontal cortex to V1, or reach both areas simultaneously. And this is just for the simple detection of a visual stimulus, not for complex attentional tasks.\n\n

What anonymous poster said about different cells having different latencies is correct. But I don't think that point is relevant to their conclusions. Buschman and Miller record the activity of many neurons and then asked which neurons in each area were the *first* to receive the attention signal. Then, they compared the latencies of the earliest neurons in each area. This tells you when the signal first arrived in each area. So the fact that there is a wide spread of latencies among neurons doesn't matter. All that matters is whether the earliest neurons in brain area X are earlier or later than the earliest neurons in area Y.\n